The present invention relates to antenna feed systems, and more specifically to quadriliar antenna feed systems.
Modem communication systems employ transceivers that are housed in satellites that orbit the earth. These systems include television broadcasting, radio broadcasting, telephone and wireless internet. These types of systems require a ground-based receiver/transceiver, or in some specialized instances, an aircraft based receiver/transceiver. For example, these systems may be in the form of a handheld device, a radio mounted in an automobile or a system in a home or business building. Each system of this type requires an antenna to provide reception/transmission of radio waves to complete the communication link between the satellite and the ground-based equipment. The antenna of choice is often the quadrifilar helix due to the radiation pattern and polarization that it produces.
A quadrifilar helix antenna is composed of four equally spaced identical helices wound on a cylindrical surface. For transmitting, the helices are fed with signals equal in amplitude and 0, 90, 180, and 270 degrees in relative phase to produce circularly polarized electromagnetic radiation. In the prior art, the helices are typically fed microwave energy by circuits containing a quadrature coupler and/or by a balun.
There are prior art methods known that provide feed networks for a quadrifilar antenna. An example is U.S. Pat. No. 5,594,461 to O""Neill which discloses the use of first, second and third transmission lines that are arranged in a xe2x80x9cZxe2x80x9d configuration. The first transmission line matches impedances between the first and second antenna elements and communicatively couples the second antenna element with a quarter wavelength phase shift of its signals to the first antenna element. The second transmission line matches impedances between the third and fourth antenna elements and communicatively couples the fourth antenna element with a quarter wavelength phase shift of its signals to the third antenna element. The third transmission line matches the resultant impedance of the coupled third and fourth antenna elements to the resultant impedance of the coupled first and second antenna elements and couples the third and fourth elements to the coupled first and second antenna elements with a half wavelength phase shift of the respectively coupled signals. A fourth transmission line matches the resultant impedance and couples the coupled first, second, third and fourth antenna elements to the load.
Another prior art example is U.S. Pat. No. 6,094,178 to Sanford which discloses a method of using a 90 degree hybrid coupler to split the signal into two paths with one path having a 0 degrees phase shift and the second path having a 180 degree phase shift. Each path leads to a balun that further splits the signal resulting in four paths that each have the desired phase.
Although the prior art methods obtain satisfactory performance parameters, there is still a need to be able to inexpensively manufacture quadrifilar antenna feed network devices that are small in size.
It is an object of the present invention to provide an improved quadrifilar antenna feed network device.
It is another object of the present invention to provide an improved quadrifilar antenna feed network device that is small in size.
It is another object of the present invention to provide an improved quadrifilar antenna feed network device that is easy to manufacture.
It is another object of the present invention to provide an improved quadrifilar antenna feed network device that is capable of being contained in a surface-mountable package.
These and other objects of the present invention are obtained by a circuit for supplying signals to a quadrifilar antenna that has an input port for receiving a first signal, a first transmission line connected at one end to the input port, and a first connection point. The first connection point is connected to another end of the first transmission line. The first connection point provides a path to a first antenna port. A second transmission line is connected at one end to the first connection point. A second connection point is connected to another end of the second transmission line. The second connection point provides a path to a second antenna port. A third transmission line is connected at one end to the second connection point. A third connection point is connected to another end of the third transmission line. The third connection point provides a path to a third antenna port. A fourth transmission line is connected at one end to the third connection point. A fourth connection point is connected to another end of the third transmission line. The fourth connection point provides a path to a fourth antenna port. The circuit provides equal amplitude at each of the antenna ports and further provides phase progression of 0 degrees, 90 degrees, 180 degrees and 270 degrees.